Changes

configure.ac: EMBEDDED modifies default AC_ARG_ENABLE values

With this patch, EMBEDDED simply modifies the default enable/disable
configure args, as in a preset, instead of changing state after checks
have been done.
This way the logic is clarified since the same logic in configure is
always checked, regardless of EMBEDDED being set or not.

Change-Id: I164eb461fb59c7675393219102740f40c1119fdd

gmstap_log: optimization: Add talloc_pool for transmitted messages

In synchronous modes (blocking and non-blocking), set a pool size of 1
msgb. This way we avoid re-allocating the msgb with malloc/free
everytime a gsmtap_log msg is transmitted over the target, and instead
we allocate the msgb during creation of the target.

In asynchronous mode (workqueue), create a pool of 100 msgbs, which
should in general be enough to speedup more usual needs. If more than
100 msgbs are to be enqueued into the gsmtap_inst, then they will be
allocated as normal talloc contexts.

Since the struct log_target is public, it is currently not possible to
add new fields to it under "tgt_gsmtap" without breaking the ABI. Hence,
the ->output field, which is unused in this target, is reused to store
the pool object internally.

Change-Id: I19cdf09f21d856e8e3646de495ce7ae040195268

select.c: Check for ENABLE_PSEUDOTALLOC instead of EMBEDDED

The reason to avoid that code is that pseudotalloc doesn't implement
that function. Hence check for pseudotalloc support specifically.

Change-Id: I9c4aa66a55beac710912db9b8d3ad9ae5c1679ef

select.c: Check for ENABLE_PLUGIN instead of EMBEDDED

Change-Id: I6cae7781a94e4eb6daaf97c16638fd933a3c9123